DESCRIPTION (Investigator's abstract) "This is a planning grant proposal to support the development and refinement of procedures protocols for a clinical trial of the efficacy of vision training (VT) in intermittent exotropia (IXT). IXT affects approximately 4,000,000 people in the United States. For nearly 100 years VT has been used clinically to treat a wide range of oculomotor, perceptual, and behavioral disorders including various types of strabismus, amblyopia, accommodative dysfunction, and visual perception deficits. The efficacy of this time-consuming and moderately expensive treatment has yet to be conclusively demonstrated for any condition. Prior attempts to develop clinical trials have suffered from the variability in the numbers and types of methods that have been employed, from the wide range of disorders treated, and from the lack of operational definitions for success. The proposed clinical trial, employing fixed protocols for eligibility, interventions, and outcomes, evaluates VT in a defined subset of strabismus (IXT). The results of this clinical trial will determine whether VT should be tested in other disorders. In the proposed multicenter clinical trial -- The VT-IXT Study -- 660 patients with IXT will be randomly allocated to one of three groups: 1) a control group that receives best refractive correction for distance vision, 2) a group that receives a VT regimen and the distance refractive correction, and 3) a group that receives a placebo VT regimen and the distance refractive correction. The primary outcome measure will be the proportion of time that the exotropia is manifested under carefully controlled test conditions at the end of a maximum of eight months of treatment. A three-year follow-up study on these patients will also examine the longevity of any benefits, the effects of additional VT treatments, and the effects of other noninvasive treatments, such as, monocular patching, prisms, and over minus-lens correction. This planning grant will provide the rationale and design for the proposed clinical trial, plus a demonstration that there will be adequate numbers of patients available for the study. During the planning period, the Manual of Procedures will be completed and studies will be performed by the Coordinating Center and selected clinics to refine the tests, protocols, and data management procedures."